Method and apparatus for high speed plastic strapping welding

ABSTRACT

An apparatus for producing an improved friction-fused welded joint is provided for use with overlapping thermoplastic strap portions. In an embodiment, the gripper is caused to swing back and force with a sufficiently large stroke and with a sufficiently fast stroke to cause sufficient reciprocation to rapidly heat the thermoplastic so that the two straps are welded together while reducing the depth of the area that is melted compared to traditional methods. Also, in an embodiment, a method is provided for stopping the relative motion of the two portions of straps with the portions of the plastic straps oriented in the same relative positions at the end of the welding operation as at the beginning is disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority benefit of U.S. Provisional PatentApplication No. 61/841,901 (Docket #BN-1), entitled “METHOD ANDAPPARATUS FOR HIGH SPEED PLASTIC STRAPPING WELDING” filed Jul. 1, 2013,by Pavlo Barsalov, which is incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to a process and an apparatus for welding strapsmade of thermoplastic plastics, particularly packaging straps made ofpolyester or the like.

BACKGROUND OF THE INVENTION

The subject matter discussed in the background section should not beassumed to be prior art merely as a result of its mention in thebackground section. Similarly, a problem mentioned in the backgroundsection or associated with the subject matter of the background sectionshould not be assumed to have been previously recognized in the priorart. The subject matter in the background section merely representsdifferent approaches, which in and of themselves may also be inventions.

Some prior art patents are U.S. Pat. No. 3,554,846 R. J. BILLETT 1971,U.S. Pat. No. 4,247,346 Kazuo Maehara, 1978, U.S. Pat. No. 4,858,815Derek A. Roberts, 1989; EP 1824738 B1, Steve Aemisegger, 2005, U.S. Pat.No. 8,070,039 B1, Stephen A. Johnson 2010, U.S. Pat. No. 8,181,841 B2,Stephen A. Johnson 2011, U.S. Pat. No. 8,376,210 B2, Stephen A. Johnson2012.

The welding process typically involves pressing one of the two strapportions against the other strap portion, so that the two strap portionsoverlap one another, with a force to create pressure holding the twostrap portions together. One of the two straps is rapidly moved relativeto the other strap to generate friction at the area of interface betweenthe two straps. The pressure and movement generate sufficient heat tocause the components to begin to melt. Once the two straps are melted atthe point of contact, the movement of the two straps is terminated, andthe two straps are allowed to cool down while under a pressure pushingthe two strap portions together. As the straps cool down in this staticcondition, a welded joint is formed at the interface where the two strapportions contact one another. The welding process may be applied topolyester strap with 16 mm width and 1 mm thickness and breakingstrength about 650 kg, for example.

Conventionally produced welded joints in thermoplastic straps have foundwide commercial acceptance in many applications. However, the weldingprocess of creating such joints has limitations. Referring to FIG. 1,one of two straps typically, lower strap 41, is the stationary strap, isloaded with tension force P during the welding operation. Theconventional welding process requires a certain period of time to meltthe material in the contact area. In that period of time, portions deepwithin the lower strap warm up, which reduces the cool cross section andtherefore dramatically lowers breaking strength of the lower portion ofthe strap. Consequently, most plastic strapping apparatuses do not allowthe strap to be tensioned more than 35% of the breaking strength of thestrap and therefore do not utilize all of the capability of thisexpensive strap.

There are known methods and apparatuses that attempt to locate thewelding surfaces in a predetermined position, by for example, using acombination of (1) forces of inertia to increase stroke from zero to amaximum and (2) a spring return mechanism to return to the initialposition. However, this method is not entirely satisfactory since springmechanisms are not able to consistently and accurately provide thealignment required. Also, there are methods of using forces of inertiawithout a spring return mechanism, but the welding mechanism is far lessreliable and stable without the spring return mechanism.

Also there are some devices that have a very reliable stroke adjustingmechanism, but this kind of mechanism is too heavy in weight and isexpensive to produce. As a result of the weight of the very reliablestroke adjusting mechanisms, the very reliable stroke adjustingmechanisms can only be implemented in stationary strapping machines andare not suitable for a mobile, handheld, or portable strappingapparatus.

All of the above-described examples utilize the same idea of adjustingstroke during the rotation of the driveshaft, which is still rotating isthe same direction.

SUMMARY OF THE INVENTION

In an embodiment, an improved welding joint using a large stroke andhigh speed welding mechanism in conjunction with a reversible weldingmotor is provided.

In an embodiment, a welding mechanism with ability of align two strapsin the beginning as well as in the end of the welding operation isprovided.

In an embodiment, a method for stopping the relative motion with theplastic straps with respect to each other is provided.

In an embodiment, a method for keeping the straps oriented in the samerelative positions at the end of the welding operation as at thebeginning is provided.

In an embodiment, an apparatus is provided that includes a particulareccentric mechanism including at least a welding motor, a motor bushing,an eccentric shaft. The welding motor is mounted on a frame. The motorbushing is fixedly attached to the rotor of the welding motor. One sideof the eccentric shaft is pivotally mounted on the frame. The other sideof the eccentric shaft is also pivotally mounted on the motor bushing.The eccentric bushing is pivotally mounted on the eccentric shaft. Theeccentric bushing is connected through the bearing to that connectingrod, which moves the upper strap. The motor bushing is connected to theeccentric bushing only in the circumferential direction and is able totransmit the torque from the motor to the eccentric bushing. Theeccentric shaft is mounted in such a way that the eccentric shaft ispermitted to assume either of two stable positions in accordance to theeccentric bushing. In the first position, the longitudinal eccentricaxis of eccentric bushing is co-axial with longitudinal rotating axis ofthe eccentric shaft and the combined eccentricity in the first positionof the eccentric bushing and the eccentric shaft is zero or relativelylow. In second position, the eccentric shaft is turned to a particularangle, which for example may be 180 degrees. In an embodiment, when theeccentric shaft is turned to this particular angle, the distance betweenthe rotation axis of the eccentric shaft and the eccentric axis of theeccentric bushing is at a maximum, which increases the eccentricity to arelatively high value or maximizes the eccentricity. Thus, in the firstposition, the rotation of the motor bushing does not move the connectingrod and consequently the straps continue to be aligned. In the secondposition, the rotation of the motor bushing results in the maximumoscillation of the eccentric bushing that is possible for the giveneccentricity of the eccentric bushing and eccentric shaft, andconsequently the reciprocation applied to the upper strap has themaximum amplitude that is possible for the combination of the eccentricbushing and eccentric shaft. Accordingly rotation of the motor shaft infirst direction results in a stationary position of two straps androtation of the motor shaft in second direction (which in an embodimentis opposite to the first direction) provides reciprocation of upperstrap with a maximum amplitude and therefore high speed welding process.In an alternative embodiment, in the second position, the eccentricshaft is rotated to make an angle with the eccentric bushing that issufficient to create enough reciprocation to weld the two straps, but isnot the maximum angle and does not provide the maximum amplitude ofoscillation.

It is preferable that in the low eccentricity configuration that theeccentricity be zero. The higher the eccentricity, the more misalignmentof the straps in the joint. In prior art misalignment could be zero ormaximum (that is about 1.2 mm) and the degree of misalignment isunpredictable. In an embodiment the value of eccentricity is certainvalue close to zero, and therefore the misalignment is zero or close tozero.

Also, the welding method provided may use a sequence of differentdirections of rotation of the motor shaft:

Rotation of the motor shaft in first direction provides neutral gripperpositioning and at the same time engages the gripper under the pressurewith the upper strap aligned with the lower strap.

Rotation of the motor shaft in the opposite (second) direction provideshigh speed welding process.

After the welding is complete, immediate rotation of the motor shaftback to the first direction provides a neutral position of the gripperengaged with the upper strap, at the same time keeping the welded jointunder the pressure. After the material in the adjacent area solidifiesand the welding joint is complete, the gripper is raised, and the strap(that until now was under tension) is released from the strapping tool.Now, the gripper, the eccentric shaft and eccentric bushing are ininitial their initial positions and the device is ready for a new cycle.

The method and apparatus for high speed plastic strapping welding areexplained in more detail with reference to examples of embodiments inthe description given below with reference to the drawings. Any of theabove embodiments may be used alone or together with one another in anycombination. Inventions encompassed within this specification may alsoinclude embodiments that are only partially mentioned or alluded to orare not mentioned or alluded to at all in this brief summary or in theabstract.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following drawings like reference numbers are used to refer tolike elements. Although the following figures depict various examples ofthe invention, the invention is not limited to the examples depicted inthe figures.

FIG. 1 is a view schematically illustrating a conventional strappingtool and a strap tightened about article;

FIG. 2 a is a schematic representation with broken-out section of partof the friction welding apparatus of the present invention in initialposition;

FIG. 2 b is a cross section of the friction welding means according tothe present invention;

FIG. 2 c is a cross section of the friction welding means in eccentricshaft area (eccentric area) in initial position;

FIG. 3 a is a schematic representation with broken-out section of partof the friction welding apparatus of the present invention in an initialposition;

FIG. 3 b is a schematic representation with a broken-out section of partof the friction welding apparatus of the present invention in thebeginning of welding process;

FIG. 3 c is a schematic representation with broken-out section of partof the friction welding apparatus of the present invention during thewelding process in maximum amplitude of oscillation shown;

FIG. 3 d is a schematic representation with broken-out section of partof the friction welding apparatus of the present invention at the end ofthe welding process when the joint solidifies;

FIG. 3 e is a schematic representation with broken-out section of partof the friction welding apparatus of the present invention in initialposition with lock arms locked;

FIG. 4 a is a cross section of the eccentric area in an initialposition;

FIG. 4 b is a cross section of the eccentric area at the beginning ofthe welding process;

FIG. 4 c is a cross section of the eccentric area during the weldingprocess;

FIG. 4 d is a cross section of the eccentric area in the end of thewelding process, while the joint is solidifying;

FIG. 4 e is a cross section of the eccentric area in initial positionwith lock arms locked;

FIG. 5 is an exploded view of the friction welding apparatus;

FIG. 6 a is an exploded view of the main elements of the eccentricmechanism in an initial position;

FIG. 6 b is a cross section view of the main elements of the eccentricmechanism in an initial position;

FIG. 7 a is an exploded view of the main elements of the eccentricmechanism during the welding process in maximum amplitude of oscillationshown;

FIG. 7 b is an cross section view of the main elements of the eccentricmechanism during the welding process in maximum amplitude of oscillationshown;

FIG. 8 a shows the mechanism for engaging and releasing gripper, in theengaged position, pushing the gripper onto a portion of the upper strap;

FIG. 8 b shows the mechanism for engaging and releasing gripper, in therelease position, allowing the welding apparatus to be removed from thestrap;

FIG. 9 a shows a cross sectional view of the mechanism for engaging andreleasing gripper, in the engage position, pushing the gripper on aportion of the upper strap (along line 8-8 of FIG. 8 a);

FIG. 9 b shows a cross sectional view of the mechanism for engaging andreleasing gripper, in the release position, allowing the weldingapparatus to be removed from the strap (along line 8-8 of FIG. 8 b);

FIG. 10 a shows a perspective view of the mechanism for engaging andreleasing gripper, in the engaged position, pushing the gripper on aportion of the upper strap;

FIG. 10 b shows a perspective view of the mechanism for engaging andreleasing gripper, in the released position, allowing the weldingapparatus to be removed from the strap;

FIG. 11 a shows a cross sectional view of the lock mechanism in unlockedposition;

FIG. 11 b shows a cross sectional view of the lock mechanism in lockedposition;

FIG. 12 a shows an isometric view of the locked mechanism in unlockposition; and

FIG. 12 b shows an isometric view of the locked mechanism in lockposition.

DETAILED DESCRIPTION

Although various embodiments of the invention may have been motivated byvarious deficiencies with the prior art, which may be discussed oralluded to in one or more places in the specification, the embodimentsof the invention do not necessarily address any of these deficiencies.In other words, different embodiments of the invention may addressdifferent deficiencies that may be discussed in the specification. Someembodiments may only partially address some deficiencies or just onedeficiency that may be discussed in the specification, and someembodiments may not address any of these deficiencies.

Rapid heating is a solution to solve the problem of the welding processlowering the breaking point of the strap, while at the same timeconsumes less energy and shortens the cooling time for the welded joint.

In order to attain the rapid heating, a given amount of heat must beapplied within a minimal time window into a segment of the two strapsthat is bounded to be relatively close to the welded interface. Highheat may be generated with the use of high frequency reciprocation(which is an oscillatory motion). However the high frequencyreciprocation is usually limited by mechanical design and is not widelyused in mobile strapping apparatuses.

Also the rapid heating can be achieved by increasing the pressurebetween two straps in the welded region, the amount of pressure isusually limited for some kinds of strap, such as polypropylene (andstraps made from other similar compounds) due to molecular structure ofthe strap.

Although the stroke of reciprocation can be increased, the trailing edgeof the vibrated strap exposes a portion of the stationary strap as theleading edge of the vibrated strap moves beyond the corresponding edgeof the stationary strap. It is desirable that the plastic straps beoriented in the same relative positions at the end of the weldingoperation as at the beginning. However, if an increased stroke ofreciprocation is applied, more attention needs to be paid to keep thestraps aligned.

FIG. 1 schematically illustrates a conventional strapping tool duringthe operation of tightening and sealing the strap overlapped about anarticle. Typically, all strapping tools constructed with three majorcomponents, which includes a tightening device 1, a sealing mechanism 2,and a base 3. The tightening device 1 includes a feedwheel 11 pivotallymounted on the pin 12. The feedwheel interacts through the upper strap41 and lower strap 42, and gripper 13. Gripper 13 is situated in thereceptacle 32 of the base 31. FIG. 1 schematically shows the sealingmechanism 2 represented by upper gripper 21 and lower gripper 22situated in the receptacle 33 of base 31 and a cutter 23 intended to cutfree end 43 of the strap 4.

During the tensioning process the gripper 13 holds the lower portion 42of the strap 4 overlapped about the article 5. Rotation of the feedwheel11 causes tightening of the upper portion 41 of strap 4 therefore thelower portion 42 of the strap 4 is loaded with full amount of tensionforce P.

FIGS. 2 a-7 b include the following components, welding motor 200, aframe 201, motor bushing 202, motor shaft 203, bearing 205, bearing 206,eccentric bushing 207, bearing 208, connecting rod 209, pin 210,vertical link 211, pin 212, gripper 213, upper link 214, pin 215, pin216, main spring 217, lock spring 220, pin 221, lock arm 222, lockbracket 223, clutch 224, pin 225, set screw 226, eccentric axis 231,eccentric shaft 240, longitudinal rotation axis 241, and longitudinaleccentric axis 242.

Referring to FIGS. 2 a and 2 b, the welding apparatus may include awelding motor 200 mounted on a frame 201. The welding apparatus may alsoinclude a motor bushing 202 fixedly attached to the rotor 203 of thewelding motor 200. An eccentric shaft 240 is pivotally mounted on theframe 201 through the bearing 205 from one side (which is the left sideof FIG. 2 b). On the other side of the eccentric shaft 240 (which istowards the right side of FIG. 2 b), the eccentric shaft 240 ispivotally mounted on the motor bushing 202 through the bearing 206.Eccentric bushing 207 is pivotally mounted on the eccentric shaft 240.The eccentric bushing 207 is connected through the bearing 208 toconnecting rod 209. Connecting rod 209 moves the upper strap through pin210, vertical link 211, pin 212 and gripper 213. The upper link 214 ispivotally mounted on the frame 201 through pin 215, and the upper link214 bears the vertical link 211 through pin 216 (see the right side ofFIG. 2 a). The upper link 214, from another side (which is on the leftside of FIG. 2 a), is pressed against main spring 217.

The apparatus shown in FIG. 2 a additionally has a lock constructed oflock spring 220, pin 221, lock arm 222, and lock bracket 223. Pin 221rests on upper link 214. The lock bracket 223 is connected to the lockarm 222 through pin 225 and to the eccentric shaft 204 through one wayclutch 224. The one way clutch 224 transmits a torque in a clockwisedirection, when eccentric shaft 204 rotates. The one way clutch 224transmits a torque in a counter clockwise direction, when lock bracket223 rotates counter clockwise and permits rotation of the eccentricshaft 204 in counter clockwise direction.

The eccentric bushing 207 is pivoted about longitudinal eccentric axis242 of the eccentric shaft 240. So the longitudinal eccentric axis 242of the eccentric shaft 240 is always co-axial with longitudinal rotationaxis 230 of the eccentric bushing 207. Consequently, when eccentricshaft 240 is in the position of FIG. 4 a, longitudinal rotation axis 241of eccentric shaft 240 is co-axial with longitudinal eccentric axis 231of the eccentric bushing 207. When eccentric shaft is changingpositions, eccentric bushing 207 rotates about eccentric axis 242 of theeccentric shaft 240, so that after rotation 180 degrees, longitudinalrotation axis 241 of the eccentric shaft 240 is at maximum distance fromlongitudinal eccentric axis 231 of the eccentric bushing 207 causinglongitudinal eccentric axis 231 of the eccentric bushing 207 to orbit asthe motor turns motor bushing 202 about longitudinal rotation axis 241of the eccentric shaft 240. The orbiting of longitudinal eccentric axis231 about longitudinal rotation axis 241 creates the oscillatory motionof eccentric bushing 207, which is translated to gripper 213.

Referring next to FIG. 2 c, the longitudinal rotation axis 241 ofeccentric shaft 240 is co-axial with motor bushing 202. The longitudinaleccentric axis 242 of eccentric shaft 240 is co-axial with longitudinalrotation axis 230 of eccentric bushing 207. At the same time,longitudinal eccentric axis 231 of eccentric bushing 207 is concentricto the bearing 208 and therefore connecting rod 209. The motor bushing202 is connected to the eccentric bushing 207 only in thecircumferential direction and is able to transmit the torque from themotor 200 to the eccentric bushing 207. The eccentric shaft 240 ismounted in such a way that eccentric shaft 240 is permitted to assumeeither of two positions, in accordance to the eccentric bushing 207. Infirst position (FIG. 2 c), the longitudinal eccentric axis 231 ofeccentric bushing 207 is co-axial with longitudinal rotation axis 241 ofeccentric shaft 240. In the configuration of FIG. 2 c, the combinedeccentricity of eccentric bushing 207 and eccentric shaft 240 is minimalor zero, if the value of eccentricity for eccentric shaft 240 andeccentric bushing 207 are equal. In second position, the eccentric shaft240 is turned to a particular angle, which may be 180 degrees from theinitial orientation of the eccentric shaft, for example. Depending onthe eccentric bushing 207 (as shown in FIG. 4 c), after turning theeccentric shaft 180 degrees, the distance between the longitudinalrotation axis 241 and longitudinal eccentric axis 231 is maximized.Therefore, in the first position, the rotation of the motor bushing 202does not move the connecting rod 209. Since connecting rod 209 does notmove in the first position, straps 41 and 42 remain aligned in neutralposition. In the second position, the rotation of the motor bushing 202causes a maximum amount of oscillation of the eccentric bushing 207. Asa result of the oscillation, the reciprocation applied to the upperstrap with maximum amount of amplitude. Accordingly, the rotation of themotor shaft 203 in a first direction results in the two straps beingheld in fixed stationary neutral position and do not move with respectto one another. Rotation of the motor shaft 203 in the second direction(opposite to the first direction) causes reciprocation that is appliedto upper strap 41 with maximum amplitude and therefore create sufficientheat to provide a high speed welding process.

The above described example of embodiment utilizes a method of operationaccording to this invention as follows:

After the strap 4 has been placed around the article 5, and after thestrap ends 41 and 42 have been inserted in the strapping tool, the strapis tensioned to a desired tension force, by tightening device with thegripper 213 in a raised position. After tensioning with the gripper inthe raised position, the welding apparatus is in the positionillustrated in FIG. 3 a. Lock arm 222 and lock bracket 223 are pressedby lock spring 220 in a counterclockwise direction, and form the lock.When lock arm 222 and lock bracket 223 are pressed by lock spring 220 ina counterclockwise direction, lock arm 222 and lock bracket 223 holdupper link 214 and therefore gripper 213 in raised position. When in thelocked position, with gripper 213 raised, the eccentric shaft 240 is inthe position illustrated in FIG. 4 a so that the eccentricity of theeccentric mechanism is zero.

In order to weld the strap ends 41 and 42, the operation mode begins byturning the motor shaft 203 clockwise (first direction). As a result,the motor shaft 203 turns the lock bracket 223 through the motor bushing202, eccentric bushing 207, eccentric shaft 240 and one way clutch 224.The movement of the lock bracket 223 overcomes the torque of lock spring220, and causes the lock arm 222 to swivel in a clockwise direction.

The swivel of lock arm 222 produces the following effects:

The eccentric mechanism is placed into a neutral position. Having theeccentric mechanism in the neutral position ensures that gripper 213 isin a neutral position.

The lock is unlocked, and the upper link 214 is allowed to moveclockwise. Moving the upper link 214 clockwise brings the gripper 213 incontact with upper strap 41 under the pressure of main spring 217 (FIGS.3 b and 4 b).

After the gripper 213 is in contact with upper strap 41, the weldingprocess begins by turning motor shaft 203 counter clockwise (seconddirection) (FIG. 3 c), which in turn puts eccentric shaft 240 inposition illustrated in FIG. 4 c and therefore sets gripper in motion.Thus, welding process occurs with maximum amplitude of oscillation.

After welding is complete, but while the material in welded area isstill soft, the motor shaft 203 immediately turns backward in theopposite direction, which is clockwise (first direction) (in FIG. 3 d).Turning the motor shaft backwards—in first direction—causes the gripper213 to be in a neutral position (as illustrated in FIG. 4 d) in whichgripper 213 is engaged with the upper strap. Placing gripper 213 so thatgripper 213 is engaged with the upper strap 41 in neutral position setsthe vertical alignment of upper strap 41 and lower strap 42 as thevertical alignment was in the beginning of the welding process. Thewelded joint is allowed to cool down under the pressure of gripper 213until material in the joint area solidifies.

In order to free the strap 4, gripper 213 rises up, upper link 214swivels counter clockwise pressing down the main spring 217 until lockarm 222 (under the torque of the lock spring 220) moves to the lockedposition shown in FIGS. 3 e and 4 e, which is the initial position. Anoperator can now remove the strap and the strapping tool is ready for anew cycle.

FIGS. 8 a and 8 b show the mechanism for engaging and releasing gripper213, in two positions. In FIG. 8 a the position of the mechanismcorresponds with FIG. 3 b (and 3 d). This is initial position forlifting the gripper 213 and compressing the spring 217. In FIG. 8 b theposition of the mechanism corresponds with FIG. 2 a (and 3 a). Anoperator lifts the handle 14 and lever 15 moving up raises the rightportion of the upper link 214 compressing the spring 217 by the leftportion of upper link 214.

FIG. 9 a shows a cross sectional view of the mechanism for engaging andreleasing gripper, in the engage position, pushing the gripper on aportion of the upper strap (along line 8-8 of FIG. 8 a);

FIG. 9 b shows a cross sectional view (along line 8-8 of FIG. 8 b) ofthe mechanism for engaging and releasing the gripper, in the releaseposition, allowing the welding apparatus to be removed from the strap.FIG. 10 a shows a perspective view of the mechanism for engaging andreleasing gripper, in the engaged position, pushing the gripper on aportion of the upper strap. FIG. 10 b shows a perspective view of themechanism for engaging and releasing gripper, in the released position,allowing the welding apparatus to be removed from the strap. FIG. 11 ashows a cross sectional view of the lock mechanism in unlocked position.FIG. 11 b shows a cross sectional view of the lock mechanism in lockedposition. FIG. 12 a shows an isometric view of the lock mechanism in anunlocked position. FIG. 12 b shows an isometric view of the lockmechanism in locked position.

It can be seen from the description above that using the high speedwelding method and the welding apparatus of FIGS. 2 a-11 b givesnumerous advantages including lower energy consumption by the weldingprocess, which in turn, enables usage of lighter and cheaper batteries,and shortens cooling time of the welding joint thereby increasingproductivity of the strapping tool. Also, as a result of having ashallower adjacent area of the welding joint that is heated, thethreshold level of the strap tension increases, which allows a fullerutilization of the strap properties. Further, having a shallower areathat is heated, enables usage of a narrower strap (as compared to were adeeper heating process used), without breaking. As a result of beingable to use narrower or thinner straps, the entire packaging process ismore economical and energy efficient. Also, in experiments applying themethod to a polyester strap with 16 mm width and 1 mm thickness andbreaking strength about 650 kg, the straps welding joint has up to a 95%of the breaking strength of the strap (compared to up to 80% inconventional tools), which in turn makes the packaging process morereliable.

This invention is not restricted to the embodiments that have beendescribed and illustrated. Rather, numerous changes and additions arepossible without departing from the scope of the invention.

Each embodiment disclosed herein may be used or otherwise combined withany of the other embodiments disclosed. Any element of any embodimentmay be used in any embodiment.

Although the invention has been described with reference to specificembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the true spirit and scope of theinvention. In addition, modifications may be made without departing fromthe essential teachings of the invention.

1. An apparatus comprising: a welding motor with a motor shaft, aneccentric shaft, a motor bushing, the motor bushing being fixedlyattached to the motor shaft of the welding motor; an eccentric bushing;the eccentric bushing engaging the motor bushing, such that rotating themotor bushing rotates the eccentric bushing; the eccentric bushing beingcoupled with the motor bushing to transmit the torque; the eccentricbushing being pivotally mounted on the eccentric shaft so that eccentricaxis of the eccentric shaft is coincident with rotation axis of theeccentric bushing; the eccentric shaft protruding into the eccentricbushing; the eccentric shaft being coupled to two stops that as a resultof the coupling, rotate with the motor shaft; the eccentric shaft beingcoupled to the vertical link; the vertical link being linked to thegripper, which contacts an upper strap, when the upper strap is present;a first stop of the two stops engaging the eccentric shaft when themotor shaft rotates in the first direction; as a result of the firststop engaging in the eccentric shaft, when the motor shaft is rotated inthe first direction, eccentric shaft is pushed into a configuration inwhich the rotation axes of the eccentric shaft is coincident witheccentric axis of the eccentric bushing creating an non-eccentricrotation of the eccentric bushing when the motor shaft rotates in thefirst direction; the coupling of the eccentric shaft to the verticallink, the non-eccentric rotation of the eccentric shaft is translated,via the coupling into a stationary neutral position of the gripper; asecond stop of the two stops engaging the eccentric shaft when the motorshaft rotates in the second direction; when the second stop engages theeccentric shaft, the eccentric shaft is pushed into a configuration inwhich the rotating axis of the eccentric shaft is not coaxial with theeccentric axis of the eccentric bushing creating a maximum eccentricityin a rotation of the eccentric shaft when the motor shaft rotates in thesecond direction; as a result of the vertical link being linked to theeccentric shaft, the eccentricity in the rotation of the eccentric shaftis translated into an oscillatory motion of the vertical link; as aresult of the vertical link being linked to the gripper, the oscillatorymotion of the vertical link causes the gripper to move back and forthmoving the piece of plastic back and forth to create friction if thepiece of plastic is present.
 2. The apparatus of claim 1, furthercomprising: a frame, the welding motor being mounted on the frame; oneend of the eccentric shaft being pivotally mounted towards one side ofthe frame; another end of the eccentric shaft being also pivotallymounted on the motor bushing towards another side of the frame.
 3. Theapparatus of the claim 1, further comprising: a connecting rod; theeccentric shaft being connected through the eccentric bushing andthrough a bearing to the connecting rod, the connecting rod beingpivotally connected to the vertical link; when the motor shaft rotatesin the first direction, the first stop of the two stops engages theeccentric shaft; and when the motor shaft rotates in the seconddirection, the second stop of the two stops engages the eccentric shaft.4. The apparatus of claim 1, a main spring; an upper link; the upperlink being pivotally mounted on the frame; the upper link beingpivotally connected to the vertical link; and the main spring pushes theone end of the upper link against the frame which pushes another end ofthe upper link towards the gripper, pushing the vertical link towardsthe gripper, pushing the gripper onto the piece of plastic, when thepiece of plastic is present.
 5. The apparatus of the claim 4, furthercomprising: a one way clutch rotatably linked to the eccentric shaft; alock bracket fixedly linked to the one way clutch; a lock arm rotatablylinked to lock bracket; the upper link being coupled to the lock arm;rotation of the motor shaft in the first direction causes the one wayclutch to move the lock bracket, which moves the lock arm, whichreleases the lock and allows the upper link to pivot so that anotherside of the upper link pushes down on the vertical link under a force ofthe main spring.
 6. The method comprising: placing the first portion ofthe plastic in contact with a second portion of plastic; turning themotor shaft in a first direction which releases the lock and allows anupper link to pivot, so that another side of the upper link pushes downon a vertical link, pushing down the gripper that engages with upperstrap under the force of main spring, such that when the first portionof plastic is in contact with the gripper, the first portion of plasticis between the gripper and the second portion of plastic; as a result ofturning the motor shaft in the first direction, the motor shaft engagingthe eccentric shaft in a first configuration in which the rotating axisof the eccentric shaft is coaxial with the eccentric axis of theeccentric bushing creating a non-eccentric neutral position of theeccentric bushing; and the non-eccentric neutral position of theeccentric bushing causing a non-oscillatory neutral position of thevertical link engaged with the eccentric bushing, causing the gripper toexert a force, resulting from the main spring, on the first portion ofplastic holding the first portion of plastic in place on the secondportion of plastic in neutral position;
 7. A method of claim 6 furthercomprising: turning the motor shaft in a second direction; as a resultof turning the motor shaft in the second direction, the motor shaftengaging an eccentric shaft in a second configuration in which therotating axis of the eccentric shaft is not coaxial with the eccentricaxis of the eccentric bushing creating an eccentricity in a rotation ofthe eccentric bushing when the motor shaft rotates; translating theeccentric rotation of the eccentric bushing to an oscillatory motion ofa vertical link engaged with the eccentric bushing, causing anoscillatory motion of a gripper, which moves a first piece of plasticover a second piece of plastic, thereby creating friction; as a resultof the friction, heating and melting a portion of the first and secondpieces of plastic in adjacent area.
 8. The method of claim 7 furthercomprising: turning the motor shaft in a first direction; as a result ofturning the motor shaft in the first direction, the motor shaft engagingthe eccentric shaft in a first configuration in which the rotating axisof the eccentric shaft is coaxial with the eccentric axis of theeccentric bushing creating a non-eccentric neutral position of theeccentric bushing; and translating the non-eccentric neutral position ofthe eccentric bushing to a non-oscillatory neutral position of thevertical link engaged with the eccentric bushing, causing the gripper toexert a force, resulting from the main spring, on the first portion ofplastic holding the first portion of plastic in place on the secondportion of plastic; while the motor shaft is turning in the firstdirection, allowing the first portion of plastic and the second portionof plastic to cool and solidify in neutral position of the gripper;after the first portion of plastic and second portion of plastic havesolidified enough so that the first portion of plastic is expected to bebonded to the second portion of plastic releasing the first portion ofplastic and second portion of plastic from the gripper.